Serological follow-up of S.mansoni infected baboons will be carried out, before and after chemotherapy, by means of the detection of circulating antigens of different origins, and also through the search of antibodies, of various isotype, directed against different antigenic structures of the parasite. This will be an attempt to find an indicative antigen- antibody system for differential diagnosis of acute or recent infections from the chronic ones, and for cure after chemotherapy. Therefore, antigenic structures of cercarium, adult worm and egg of S. mansoni, as well as, some purified fractions and DNA-recombinant antigens will be related to IgG subclasses, IgM, IgA and IgE antibodies, by using immunofluorescence (IF) and immunoenzymatic assays (ELISA, DOT-ELISA, Immunoblotting). Some serological tests, selected by means of their ability for discriminating active from passive (that is cured) or recent from chronic S. mansonia infection in baboons, will be os potential value for the diagnosis in human infection.